Research Into The Structural Form Of Underground Gas Storage Chambers Based On The Long-term Stability Of The Surrounding Rock

With the continuous advancement of China’s "dual-carbon" goal,the form of energy structure is gradually transformed into new and clean energy,thus replacing traditional energy.At the same time,it will cause problems in the supply and demand of natural gas and the wide application of compressed energy storage technology in the future.The construction of large underground gas storage caverns can effectively alleviate or solve the above problems.However,most of the gas storage caverns in China are built under salt rock geological conditions,and the cavern projects built under hard rock conditions are relatively limited.Therefore,higher requirements are put forward for the construction of gas storage caverns under hard rock geological conditions.Especially in the early stage of the construction of the gas storage cavern,the reasonable structural form can make the best use of the underground space and have a small impact on the stability of the surrounding rock.The research on the safety and stability problems caused by the construction of gas storage caverns under hard rock conditions can provide meaningful reference value for the future construction and operation of underground gas storage caverns in China.Therefore,this thesis studies the mechanical properties of typical cavern rock by means of experimental methods,and studies the possibility of building gas storage cavern under hard rock conditions and the stability of surrounding rock under long-term operation through theoretical analysis and numerical simulation.The main research contents and conclusions of this paper are as follows :(1)The indoor conventional compression tests under different axial stresses and confining pressures were carried out on the on-site sampling rock samples.Based on the test results,the stress-strain curve variation law and the failure state of the rock sample under various conditions were analyzed.The basic mechanical parameters such as elastic modulus,Poisson ’s ratio,internal friction angle and cohesion of the rock sample were obtained.At the same time,the triaxial compression creep test was carried out on the field rock samples,and the stress-strain curve under the condition of graded incremental load with the same confining pressure was analyzed to obtain the variation law of axial strain with time.The fitting analysis of the experimental data and the theoretical curve of the H-K rheological model shows that the model can better reflect the creep characteristics of rock samples and the relevant parameters of the model.(2)Based on the results of conventional indoor compression test and the stressvolume strain curve inflection point method,the stress state of the expansion failure of the rock sample is determined.Based on the salt rock expansion failure criterion,the parameter correction is carried out to obtain the expansion failure boundary equation of the rock sample,and the safety factor of rock expansion failure around the tunnel is proposed by using the equation.(3)Using numerical simulation methods,the long-term stability of the gas storage chamber is studied.The variation law of the displacement around the gas storage chamber,the maximum rheological displacement deformation around the chamber,and the safety factor of the rock expansion failure around the chamber with the heightdiameter ratio,the thickness of the cover layer and the chamber spacing are analyzed.The recommended values of the height-diameter ratio,the minimum cover layer thickness and the chamber spacing of the gas storage chamber are given under the condition of a certain capacity of the gas storage chamber under high internal pressure.At the same time,the limit internal pressure of gas storage under different overburden thickness is also obtained.(4)The numerical simulation method is used to study the single gas storage chamber and the gas storage chamber group under the condition of constant pressure and cyclic injection-production gas pressure.Based on the numerical simulation results,the variation law of the maximum rheological displacement deformation and the expansion failure of the surrounding rock with the internal pressure of the gas storage is analyzed.Under the appropriate operating pressure,the longer the running time,the more conducive to the stable long-term operation of the gas storage chamber;at the same time,the variation law of deformation around the tunnel is related to the change of cyclic gas injection and production mode,and the maximum internal pressure of gas storage should be controlled during operation.